the-independent-friend.de has both AAAA (IPv6) and A (IPv4) records. While they both appear to be accessible on the network, we have detected that they produce differing results when sent an ACME HTTP validation request. This may indicate that the IPv4 and IPv6 addresses may unintentionally point to different servers, which would cause validation to fail.
[Address Type=IPv4,Response Code=404,Server=nginx/1.12.2] vs [Address Type=IPv6,Response Code=404,Server=Apache]